The GitBook Integration Platform is currently in alpha. It's not opened to developers just yet.
References for the command line utility gitbook. The program can be used to create, test and publish integrations for the platform.
Install using npm install @gitbook/cli -g.

gitbook auth

Authenticate the CLI with a API token. The token can be provided using the command line argument --token=<token>; if none is provider, it'll be prompted.

gitbook init <dir>

Create and initialize a new integration locally. The program will prompt for information about the integration.

gitbook publish <manifest>

Publish the integration defined in the <manifest> YAML file.

gitbook whoami

Print information about the currently authenticated user.